Nanostructured Ferroelectric‐Polymer Composites for Capacitive Energy Storage

Abstract

offer a high power density to meet the demand in rapid charge-discharge applications. [6][7][8][9] Supercapacitors exhibit higher power densities and long cycling lifespans, but are limited by the chemical and electrochemical stability of the electrolytes, as well as a relatively low operating voltage. [10][11][12][13] Polymer film capacitors possess the advantages of low cost, facile fabrication, excellent flexibility, and high operating voltage, display the highest power densities in comparison with batteries and supercapacitors, and are widely used in electronic devices and power systems. [14][15][16][17][18] Although the state-of-the-art capacitor film represented by biaxially oriented poly propylene (BOPP) exhibits ultrahigh charge-discharge efficiency, the energy density has been significantly limited by its low dielectric constant (K), which is only about 1-2 J cm −3 . [19] To address this issue, ferroelectric polymers represented by poly(vinylidene fluoride) (PVDF) and its copolymers and terpolymers with relatively high K (≥10) have been regarded as the most promising polymeric materials for high-energy-density film capacitors. [16][17][18][19][20][21][22][23] More importantly, since capacitors can contribute more than 25% of the volume and weight to the electric power systems, the dramatic improvement of energy density of film capacitors will help to reduce the volume, weight, and cost of electronic devices, hybrid electric vehicles, etc. [24,25] The K value of ferroelectric polymers, however, is still considerably low in comparison with those of ceramic dielectrics (e.g., K of 10 4 -10 5 ) for capacitive energy storage, though these ceramics suffer from low dielectric-breakdown strength (E b ) and poor scalability. [26][27][28][29] Thus, a composite approach has been developed to improve energy-storage capability via introducing high-K inorganic fillers into ferroelectric polymers with high E b and facile processability. For dielectric polymer nanocomposites, the total stored energy densities, which are the sum of the energy densities of the ceramic filler and the polymer phases, are derived from, where U d is the energy density, f 1 is the volume fraction of the ceramic filler, f 2 is the volume fraction of the polymer matrix, and g is the interfacial area between the filler and the polymer. As ferroelectric polymers have the highest energy densities among the known dielectric polymers, they have been considered as the material of choice as polymer-matrix candidates for dielectric polymer nanocomposites. Moreover, the relatively high K values of ferroelectric polymers help to alleviate local field distortion in the The introduction of inorganic components into a polymer matrix to form polymer composites is an emerging and promising approach to dielectric materials for capacitive energy storage. Ferroelectric polymers are particularly attractive as matrices for dielectric polymer composites owing to their highest dielectric constant (≥10) among the known polymers. Here, the important aspects and recent ...

Tuning Nanofillers in In Situ Prepared Polyimide Nanocomposites for High‐Temperature Capacitive Energy Storage

“…[ 4,5 ] While dielectric ceramics are traditional materials for high‐temperature capacitors, [ 6 ] they are severely limited by scalability, weight, fracture toughness, and breakdown strength in comparison to their polymer counterparts. [ 7–17 ] Biaxially oriented polypropylene film (BOPP), the state‐of‐the‐art commercially available polymer dielectric, however, shows largely degraded high‐field dielectric properties when operating at temperatures above 100 °C. [ 18 ]…”

Ternary polymer nanocomposites with concurrently enhanced dielectric constant and breakdown strength for high‐temperature electrostatic capacitors

“…As excepted, BTNP fillers give rise to higher K of the composites relative to the PEI filled with the same content of BNNS, which is attributed to the greater K of BT comparing with BN (>60 vs 4-4.5). 7,9,10 As the inorganic fillers with higher K usually exhibit greater dielectric loss, tan δ of the composites increases from 0.0084 of the neat PEI to 0.0117 of the PEI composite with 1.69 vol% BNTP fillers. Conversely, the addition of wide band-gap (~6 eV) BNNS fillers can effectively reduce tan δ of the composites, 14,38,39 which reaches the minimum value of 0.0053 at 7.26 vol% filler content.…”

“…Moreover, compared with electrochemical energy storage devices such as batteries and supercapacitors, the electrostatic capacitors store less energy per unit volume, which fail to meet increasing demands of high energy densities required by advanced energy systems. 9,24 For linear dielectrics, the discharged energy density U e = 1/2DE = 1/2ε 0 KE, 2 where D is the electric displacement, E is the applied electric field, ε 0 is the vacuum permittivity (8.85 × 10 −12 F m −1 ), and K is the dielectric constant. Therefore, U e is highly dependent on both K and E, where E limited by the breakdown strength of dielectrics.…”

Crosslinked fluoropolymers exhibiting superior high-temperature energy density and charge–discharge efficiency

“…1,2 Polymers generally display the characteristics of thermally activated charge transport, leading to sharply increased leakage currents with increasing temperature. [3][4][5] Consequently, while polymer dielectrics are the preferred materials for energy storage capacitors owing to their high breakdown strength and low loss, [6][7][8][9][10][11][12][13][14][15][16] their performance typically optimized for operation at ambient temperature declines significantly with the increase of working temperatures. [17][18][19][20] For example, the discharge efficiency (η, η = U e /U o × 100%, U e : discharged energy density, U o : stored energy density) of biaxially oriented polypropylene (BOPP) films, which is the best commercially available dielectric polymer, decreases steeply from 96.2% to 87.4% and 68.5% with increasing temperature from 25 o C to 80 o C and 120 o C, respectively, at an applied field of 400 MV m -1 .…”